Thermal processing systems, such as laser and plasma arc systems, are widely used in the cutting, welding, heat treating, and processing of metallic materials. A laser-based apparatus generally includes a nozzle through which a gas stream and laser beam pass to interact with a workpiece. Both the beam and the gas stream exit the nozzle through an orifice and impinge on a target area of the workpiece. The laser beam heats the workpiece. The resulting heating of the workpiece, combined with any chemical reaction between the gas and workpiece material, serves to heat, liquefy and/or vaporize a selected area of workpiece, depending on the focal point and energy level of the beam. This action allows the operator to cut or otherwise modify the workpiece.
A plasma arc torch generally includes a cathode block with an electrode mounted therein, a nozzle with a central exit orifice mounted within a torch body, electrical connections, passages for cooling and arc control fluids, a swirl ring to control fluid flow patterns in the plasma chamber formed between the electrode and nozzle, and a power supply. The torch produces a plasma arc, which is a constricted ionized jet of a plasma gas with high temperature and high momentum that exits through the nozzle orifice and impinges on the workpiece. Gases used in the torch can be non-reactive (e.g., argon or nitrogen), or reactive (e.g., oxygen or air).
In general, a thermal processing system includes a laser-based or plasma-based torch, an associated power supply, a gas console, a positioning apparatus, a cutting table, a torch height control, and an associated computerized numeric controller (CNC).
In operation, a user places a workpiece on the cutting table and mounts the torch on the positioning apparatus, which provides relative motion between the tip of the torch and the workpiece to direct the laser beam or the plasma arc along a processing path. The user provides a start command to the CNC to initiate the cutting process. The CNC accurately directs motion of the torch and/or the cutting table to enable the workpiece to be cut to a desired pattern. The CNC is in communication with the positioning apparatus. The positioning apparatus uses signals from the CNC to direct the torch along a desired cutting path. Position information is returned from the positioning apparatus to the CNC to allow the CNC to operate interactively with the positioning apparatus to obtain an accurate cut path.
The power supply provides the electrical current necessary to generate the laser beam or the plasma arc. The power supply has one or more dc power modules to produce a constant current for the torch. Typically, the current can be set to discreet values. The power supply has a microprocessor, which regulates essentially all torch system functions, including start sequence, CNC interface functions, gas and cut parameters, and shut off sequences. For example, the microprocessor can ramp-up or ramp-down the electrical current. The main on and off switch of the power supply can be controlled locally or remotely by the CNC. The power supply also houses a cooling system for cooling the torch.
The gas console controls flow of gases to the torch. The gas console houses solenoid valves, flow meters, pressure gauges, and switches used for gas flow control, which for the plasma-based torch includes plasma gases and shield gases. The flow meters are used to set the preflow rates and cut flow rates for the plasma and shield gases. The gas console also has a multi-inlet gas supply where the required gases can be connected. A toggle switch can be used to select the gases. The gases are monitored by gas pressure gages. To operate the gas console, all settings typically are manually selected.
The torch height control sets the height of the torch relative to the work piece. The torch height control, typically, has its own control module to control an arc voltage during cutting by adjusting the standoff (i.e., the distance between the torch and the work piece), to maintain a predetermined arc voltage value. The torch height control has a lifter, which is controlled by the control module through a motor, to slide the torch in a vertical direction relative to the work piece to maintain the desired voltage during cutting.
Manufacturers of thermal processing systems typically act as system integrators of components. Thermal processing systems are designed such that the control functions of the system are centralized at the CNC. The other components on the system's network operate based on the commands issued by and transmitted from the CNC. Because hardware and software for client networking does not exist for thermal processing systems, each component typically has its own customized electrical hardware and/or software interface based on a customer's specification. These interfaces use contention-based network access methods (i.e., non-deterministic access methods) for transmitting data between components. Contention-based networks require each component to test the transmission medium in order to see if it is in an acceptable state before transmitting data. As a consequence, timely access is not guaranteed and possible data collisions are possible if two devices send data simultaneously. As a result, contention-based networks limit the speed and reliability of a system.